: small cell; small round dark nucleus with dense clumps of chromatin, sometimes with halo; look like fried egg; cytoplasm does not contain GFAP; found in white matter; primary function = myelination

extends processes to myelinate multiple axons (3-8); Schwann cells extends one process to only one axon

tendency to cluster in the white matter and around neuronal perikarya and blood vessels (referred to as satellites or perineuronal satellite cells) – unknown function in these locations

Pathology of the Oligodendroglial Cell

delicate cells vulnerable to immunologic injury, responds to injury by dying (results in myelin loss); cell type most vulnerable to ischemia/anoxia in the white matter

Multiple Sclerosis

Þ demyelinating disease Þ oligodendrocytes drop out

possibility of regeneration

Þ may be capable of proliferation and (limited) remyelination within the CNS

inclusions – JC virus

Þ PML

Ependyma

Normal Structure/Function

: ciliated astrocyte-like cells that line the ventricular system; do not form a barrier to fluid

Tanycytes

Þ subtype, very elongate processes that terminate on capillaries; Only found in floor of 3rd ventricle; May mediate communication between ventricular system and the blood Þ "ventricular route hypothesis": tenycytes pick up active compounds secreted into the ventricular system and deliver them to their target circulations

Pathology of Ependyma

respond to injury by sloughing off and cannot reproduce themselves Þ result in subependymal nodules

: arise from invagination of ependyma into the ventricular cavities by the blood vessels of the pia mater; choroidal epithelium is composed of a single row of epithelial cells, thrown into villi around a core of blood vessels; specialized for fluid transfer Þ one way flow

tight junction formation with CSF production (500 cc per day); not only source of CSF production but majority

Pathology of the Choroid Plexus

99.9% of hydrocephalus is due to obstruction; but theoretically, can result from overproduction from choroid plexus

in necrotic/demyelinating processes, microglia become macrophages and phagocytize myelin and cellular debrise; if blood-brain barrier is broken down, the macrophage population is derived from circulating monocytes